Yes, use a smaller document size.
You have a huge size document, in terms of pixel dimensions and that's why the gradient is taking so long to complete.
Where it says 0.7% is the percent view as compared to 100% view on your screen.
Anyway, go to File>New and try something smaller like one of the Web presets so you something smaller to work with.
Thanks, I forgot, I remember now to put pixels on a photoshop document, thanks!